iOS: Replace find with actual filenames listed.
iOS: Replace find with actual filenames listed.

Some build tools downstream breaks since find on Linux
doesn't support the -E flag.
Shell commands also shouldn't be executed as part of GYP unless there's
no other way around the problem.

NOTRY=True

Review-Url: https://codereview.webrtc.org/2008693002
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#12858}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 7e9274638e35ceda1f836be74fb7a9b128033d78

Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk,jchavanton/webrtc,Alkalyne/webrtctrunk,jchavanton/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk,jchavanton/webrtc